Government ministers have turned on the European Research Group - accusing them of "treachery" and acting as a "party within a party."

Business minister Richard Harrington accused the ERG, led by Jacob Rees-Mogg, of “treachery” and said they were “not Conservatives” and should join former UKIP leader Nigel Farage’s new Brexit Party.

In an interview with parliament’s The House magazine, conducted before the vote, he said they had celebrated after May was defeated in last month’s vote and were not true Conservatives.

“The prime minister has done a pretty good job of standing up to them up till now, but they were drinking champagne to celebrate her losing her deal and I regard that as being treachery,” he said.

“I read that Nigel Farage is setting up a new party called Brexit and if I were them I’d be looking at that, because that seems to reflect their views more than the Conservative party does.

“They should read carefully what that party’s got to offer, because in my view they’re not Conservatives.”

Defence minister Tobias Ellwood accused the ERG of acting as “a party within a party” and described their behaviour as “provocative”, and backbencher Jonathan Djanogly said they were seeking to “pull the UK off the cliff”.

He added that he had seen nothing to show the government had the determination to stop it.

Tory MP Anna Soubry said May needed to stand up to the group she described as the “purple Momentum”, a reference to left wing grassroots group which helped propel Jeremy Corbyn to the Labour leadership.

“If she carries on like this, then we all know what is going to happen.

“Our party will become yet again unelectable and we will fall into the wilderness,” she told BBC’s Newsnight.

Meanwhile a leading Tory Remainer has claimed a dozen or more government ministers could quit by the end of the month if Theresa May refuses to extend the Brexit negotiating period beyond March 29.

The former attorney general Dominic Grieve said that the next round of Brexit votes on February 27 would be a “high noon” moment when resignations on this scale - which he said could include six cabinet members - might bring May’s government down.

He was speaking as Foreign Office minister Alistair Burt made clear his unwillingness to accept a no-deal departure, telling hardline Brexiteers in a tweet: “We are not leaving without a deal. If you want to leave, you’d better agree one. In the next fortnight would help.”

Leader of the Commons Andrea Leadsom did not discount the possibility of ministerial-level resignations, telling Radio 4’s Today programme: “Resignations from government do happen... People have very, very strong, heartfelt views about leaving the EU or remaining within it. That is a matter for them as individuals.”

But she insisted: “The vote yesterday didn’t change anything. The government’s position remains to resolve the issues of the backstop and then come back to parliament with a fresh meaningful vote. It’s essential we crack on with that work, and that’s what we are doing.”

ERG deputy chairman Steve Baker dismissed the row over Thursday’s vote as a “storm in a teacup”.

Brexiteer MPs who abstained were not prepared to be associated with the “catastrophic and foolish negotiating error” of taking a no-deal Brexit off the table, he said.

He accused May of “reinterpreting” last month’s vote, which authorised her to replace the backstop with alternative arrangements to avoid a hard border in Ireland.

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